Support for OpenPGL project

The Open Path Guiding Library is now a sandbox stage ASWF project:

https://github.com/OpenPathGuidingLibrary/openpgl

In order to add a ci-openpgl build container, we need to:

- identify the list of dependencies
- create a Conan recipe to build it as a Conan package

A custom recipe can be developed for this project, but it would be great to see a generic recipe submitted to the Conan Center Index:

https://github.com/conan-io/conan-center-index

Start by reviewing the OpenPGL repository and the Conan Center Index guidance linked in the issue. Identify OpenPGL's dependencies, then determine the Conan recipe and ci-openpgl build-container changes needed. Done means OpenPGL can be built as a Conan package in the container, with a generic Conan Center Index recipe considered where appropriate.

Written by the indexing model from the issue text.